Gardai spent six months interviewing more than 50 people and also called in the Garda Ombudsman after Donegal County Councillor Seamus O Domhnaill claimed former Mayor Frank McBrearty Jnr had assaulted and threatened him during a break in a council meeting.

Mr McBrearty rose to national prominence when he was cleared by the Morris Tribunal – which found that gardai had attempted to frame him for the murder of a man in October 1996 in the Donegal town of Raphoe.

It later emerged that cattle dealer Richie Barron had not been murdered at all, and probably died as a result of a traffic accident. Mr McBrearty was later awarded €2.5m in damages by the State.

Both sides accept there was a heated row as councillors met for a budget workshop in Lifford on October 21 last year.

In a corridor outside the chamber, Mr O Domhnaill had alleged he was assaulted and threatened by McBrearty.

However, officers did interview 28 other county councillors – as well as members of staff of the council and members of the public.

"After months of trivial, pointless, and redundant questioning, not to mention the unnecessary garda manpower which this whole non-event involved, I have been told by the DPP that I will not be prosecuted," said Mr McBrearty.

He added: "The unnecessary anxiety and strain which these allegations have placed upon my family and myself, only served as an unwelcome reminder of the cruelties and injustices which we as a family have faced in the past."